(Not Applicable)
(Not Applicable)
The present invention relates generally to valves and, more particularly, to a uniquely configured retractable plug assembly which is specifically configured to mitigate the erosive effects of abrasive fluids flowing within a valve employing linear motion valve trim.
There is currently known in the prior art, valves which include shafts and plugs that are linearly displaced during normal operation of the valve. Within these valves, which are often referred to as linear displacement valves, the plug body is disposed and movable within a disk stack or valve cage which defines a multiplicity of tortuous or non-tortuous fluid passageways. Certain linear displacement valves are configured for xe2x80x9cover plug flowxe2x80x9d wherein fluid flows radially inward into the interior of the valve cage from the exterior thereof, with the fluid undergoing a pressure drop as a result of the flow through the valve cage. In this arrangement, the valve is opened by lifting the plug body off a seat ring which thus allows the fluid to flow from the interior of the valve cage and out of the valve via the unblocked seat ring. Conversely, the movement of the seating surface of the plug body into sealed engagement with the complementary seating surface of the seat ring facilitates a closed or shut-off condition for the valve.
Over plug flow linear displacement valves are sometimes employed in applications wherein an erosive fluid (e.g., water with abrasive sand) is channeled therethrough. In these particular applications, when the erosive fluid flows from the outside of the valve cage to the inside thereof and exits the fluid passageways defined by the valve cage, the resultant jets erode the seating surface on the plug body. When the eroded plug body""s seating angle (defined by its seating surface) makes contact with the seating angle on the seat ring (also defined by its seating surface), valve shut-off is compromised and leakage occurs. The constant leakage of the erosive or abrasive fluid further accelerates the erosion damage to the seating surface of the plug body.
The present invention specifically addresses the above-described erosion damage problem by providing a retractable plug assembly with a unique configuration specifically adapted to prevent the fluid jets exiting the valve cage from directly impinging the seating surface of the plug body and to slow the erosive fluid as it passes over the seat ring. These, and other features of the present invention, will be described below.
The retractable plug assembly of the present invention is adapted for use in a valve arrangement comprising a valve housing having an upper section and a lower section. The lower section defines an interior chamber and a flow opening. The valve housing further includes a seat ring which is engaged to the lower section and at least partially disposed within the flow opening. Also included in the valve housing is an annular valve cage which is affixed to the lower section. The seat ring defines a seat ring seating surface.
The retractable plug assembly of the present invention includes a plug body, a plug housing, a retainer ring, a sacrificial wear ring, a spring retainer, and a valve spring. The plug body defines a plug body seating surface which is configured to be complementary to the seat ring seating surface. The plug body slides axially within the plug housing. The wear ring is affixed to a lower end of the plug housing by the retainer ring. The valve spring is disposed adjacent an upper portion of the plug body and is captured between the spring retainer and the plug housing.
The retractable plug assembly may be moved between a closed position and an open position in order to regulate the flow of fluid. In the closed position, the plug body seating surface is directly engaged with the seat ring seating surface which effectively blocks the radially inwardly flow of fluid through the valve cage and out of the flow opening. As indicated above, in the over plug flow arrangement, fluid flows into the interior chamber and thereafter radially through the valve cage from the exterior to the interior thereof. The flow of an abrasive or erosive fluid through the valve cage into the interior thereof occurs when the plug body is moved to its open position. Such a flow of abrasive fluid would normally result in the erosion of the plug body seating surface due to the impingement of the jets which exit the valve cage thereagainst.
Advantageously, in the present invention, the retractable plug assembly includes the wear ring extending downwardly from the plug housing. The wear ring defines a wear ring bottom face that is positioned downwardly relative to the plug body seating surface such that the wear ring bottom face is at a lower level than the plug body seating surface when the retractable plug assembly is in the open position. The seat ring defines a seat ring top face with the wear ring bottom face being configured to be complementary to the seat ring top face.
The valve spring of the retractable plug assembly is configured to bias the plug body away from the seat ring during initial engagement of the wear ring bottom face to the seat ring top face such that the radially inwardly flowing fluid exiting the valve cage is prevented from directly impinging the plug body seating surface. The valve spring is further configured to resiliently deform during downward movement of the plug body such that the plug body seating surface may thereafter directly engage the seat ring seating surface to create a fluid-tight seal therebetween in the closed position. The fluid-tight seal between the plug body seating surface and the seat ring seating surface facilitates a complete shut-off for the valve arrangement.
In this manner, the radially inwardly flowing abrasive fluid exiting the valve cage is blocked by the engagement of the sacrificial wear ring with the seat ring such that the jets may not directly impinge and erode the plug body seating surface while the plug body moves from the open to the closed position, and vice versa.